1. Field of the Invention
The present invention relates to a power generation controller for controlling power generating operation of a vehicle generator mounted on a passenger car, a truck or the like.
2. Description of Related Art
An output terminal of a vehicle generator is connected to a terminal of a vehicle battery through a charge cable for charging the vehicle battery. If the charge cable breaks or comes off the output terminal of the vehicle generator, the vehicle battery is prevented from being charged, as a result of which not only various electric devices mounted on a vehicle are made unusable, but it also becomes difficult to run the vehicle, because engine control cannot be performed normally. Accordingly, it is known, as disclosed in Japanese Patent Application Laid-open No. 7-15886, to provide a power generation controller with a function of giving warning to a vehicle driver when the charge cable breaks or comes off the output terminal of the vehicle generator by lighting a warning lamp. The power generation controller disclosed in this patent application is configured to light the warning lamp when a voltage applied from the vehicle battery to the warning lamp through an ignition switch become lower than a predetermined voltage. Since the vehicle battery can supply electric power to an engine control unit etc., for a short time after the charge cable breaks or comes off the output terminal of the vehicle generator, the vehicle driver can reconnect the charge cable or replace the charge cable at a nearby service garage before the vehicle becomes unable to travel.
However, the power generation controller having such a function as disclosed in Japanese Patent Application Laid-open No. 7-15886 cannot cope with a case where the charge cable is perfectly connected to the output terminal of the vehicle generator, but the power generation controller is imperfectly connected to this output terminal of the vehicle generator. In this case, the warning lamp is not lit, since the voltage supplied to the warning lamp from the vehicle battery is not lowered. The imperfect connection between the output terminal of the vehicle generator and the power generation controller can cause overcharging of the vehicle battery, because the power generation controller commands the vehicle generator to raise the output voltage by a value depending on a drop of the voltage supplied to the power generation controller through the output terminal of the vehicle generator, which is caused by large contact resistance between the output terminal of the vehicle generator and the power generation controller.
It is possible to avoid the overcharging of the vehicle battery by regulating the output voltage of the vehicle generator at a certain target voltage. However, in this case, there arises another problem in that the vehicle battery is undercharged, because a voltage which the power generation controller applies to an excitation winding of the vehicle battery is reduced by an amount of the voltage drop caused by the large contact resistance between the output terminal of the vehicle generator and the power generation controller.